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Analysis of water drawn from the on-site domestic well on Parcel 1, illustrates a concentration of nitrate at 34 ppm NO3. Per the requirements of the Environmental Health Department, DBCP was also analyzed and found to be non-detect(ND) in the well water. There is no potential impact to surface waters in the area, particularly the San Joaquin River. [6] CONCLUSIONS The percolation test results indicate any future septic system should have an 8,000 to 10,000 square foot leachfield area. Due to the high water table, sumps or seepage pits cannot be installed. It is our recommendation that for any proposed future septic system, a perc test should be performed in the specific location to ensure adequate effluent acceptance. The Permit Applications for additional drainage for the study area indicates a large leachfield is warranted. This is particularly important if the residence will have three or more children or four or more bedrooms. A 50% standby replacement area must also be incorporated into the design. A 50% replacement area is already incorporated into the existing system. The referenced leachfield area will help ensure stability and guard against leachfield failure. A failure would primarily result from the formation of a "biomat" or"clogging mat" on the wetted soil where the effluent enters the soil. This mat is composed mostly of aerobic and anaerobic bacteria and bacterial products consisting of a slime of polyuronides and polysaccharides. If the soil/effluent interface is well aerated, a variety of soil microfauna such as nematodes and protozoa may digest the clogging mat bacteria. This biological activity may be somewhat impeded by the clay soil structure. If it is desired to theoretically maximize the life of the leachfield, it may be designed as two separate fields. A manual diversion valve may be installed to "rest" one leachfield while the other is active. This is particularly beneficial in clay soils. It appears agricultural practices have influenced the nitrate groundwater concentration of the aquifers which serve the domestic well. The Maximum Contaminant Level (MCL) is 45 ppm nitrate. We recommend that the domestic well be monitored yearly. If levels exceed the MCL, bottled water should be used for drinking water. VaCley Arg Pgearck